1. Field of the Invention
This invention relates generally to the dissolution of polymers in water and, more particularly, this invention relates to a method and apparatus for rapidly dissolving dry, water soluble polymers in water.
2. Description of the Prior Art
The use of solutions of water soluble polymers in thickening and flocculating applications is well known. Such applications include the clarification of aqueous solutions in mining, papermaking, and in treatment of sewage and industrial wastes. Such solutions of polymers are also useful as stabilizers for drilling muds, and in the secondary recovery of petroleum by water flooding.
Although these polymers are most often available commercially as powders or as finely divided solids, they are most frequently utilized in aqueous solutions. This necessitates that the solid polymer be dissolved in water. Although the various polymers are more or less soluble in water, difficulty is often experienced in preparing aqueous polymer solutions because of their slow rate of dissolution and because the solid polymer is not readily dispersible in water.
Furthermore, dissolution of solid polymers in water is hindered by the tendency of polymer particles to clump or remain as agglomerates on contact with water. Lumps of solid polymer immediately form after limited wetting with water by the encapsulation of undissolved solids in an outer coating of water-wet polymer which retards the penetration of additional water into the agglomerate. Although many of these lumps are eventually dissolved by continued agitation, it is frequently impractical to agitate the solution for a sufficiently long period to obtain complete dissolution. Long mixing times, of course, are uneconomical and may damage the molecular weight of already dissolved polymer through exposure of the polymer to excessive hydraulic and mechanical shear.
The problem is compounded by the fact that dry polymer particles usually include very fine, dustlike particles. This creates pollution problems in the vicinity of the equipment and can aggravate the problem of buildup of sticky or slippery polymer on equipment surfaces.
Some of the foregoing problems are described in numerous prior publications, including U.S. Pat. No. Re. 28,474 (July 8, 1974) and U.S. Pat. No. Re. 28,576 (Oct. 21, 1975) issued to Anderson et al.
The above-identified Anderson et al. reissue patents exemplify prior approaches to overcoming the problem of rapidly dissolving polymers in the water. In the Anderson et al. disclosures, water soluble polymer is dispersed into a water-in-oil emulsion, which emulsion is then inverted in water to release the polymer into solution.
The method of the Anderson et al. disclosures is limited in terms of the polymer content of the emulsion. Further, such systems, in practice, require substantial amounts of an emulsifier to provide a stable product and, of course, require the use of an oil phase, which creates handling and economic problems.
Other prior methods do not rely on inversion of a polymer dispersion from an emulsion, but utilize simple mixing of polymers with water. This requires long mixing times which, in turn, require mixing and storage facilities for large volumes of solution. As a result, long storage and/or mixing times are required between the time that dry polymer is initially mixed with water and the solution thereof can be used, and capital investment and energy costs are high.